It is well known that various organic polymers undergo deterioration of physical properties and color changes during processing and during exposure of the formed polymer products to various and use environmental conditions. This deterioration of physical properties and color change is particularly pronounced in some polymers (e.g. halogenated polymers) upon their exposure to heat during processing, particularly the processing into formed articles of commerce. Undesirable color changes are observed to occur at the early stages (e.g. within the first 5 to 10 minutes) of the elevated temperature processing of the polymer as well as during the prolonged exposure of the polymer to heat during processing. Sometimes haziness or cloudiness accompany the color changes of the polymer and is particularly undesirable where clear or colorless products are needed. In many methods for making a polymer into a finished product the polymer remains in the processing apparatus, exposed to high temperatures, for a short period of time and therefore the color change or discoloration of the polymer resulting from prolonged exposure to heat during processing becomes only a minor consideration. The color change of the polymer during such short exposure to heat during processing has become known as early color and is of importance in the shaping of polymers into various products (e.g. pipe), particularly products which are to be light in color.
Early color is often manifested in various degrees of yellowing of the polymer, although other coloration has also been observed in early color problems. The problem of early color has received increasing attention in recent years and has become a significant consideration in the stabilization of polymers. However, there remains considerable need for improvement of the early color heat stabilization, as well as the long term heat stabilization, of polymers.
In the heat stabilization of organic polymers (e.g. halogen containing organic polymers) early color and long term color formation have been attacked by the art with various stabilizers, mixtures of stabilizers and stabilizer compositions. Organoantimony compounds have been used by the art alone or in combination with various other materials. Such organoantimony compounds are disclosed in, for example, U.S. Pat. Nos. 2,680,726; 2,684,956; 3,340,285; 3,399,220; 3,466,261 and 3,530,158. Vinyl halide polymers are also known to be stabilized against heat by reacting them with mercapto-phenolic compounds (see U.S. Pat. No. 3,875,084). These mercapto-phenolic compounds have the formula: ##STR1## in which each R.sub.1 is independently selected from hydrocarbyl, nitro and halogen; and n is 0 to 4. However, it has been found that these mercapto-phenolic compounds are, in fact, very poor stabilizers for vinyl halide resins. They produce a pink color when mixed with the polymers and the resulting mixture is subjected to heat.